This invention relates to a directional light-shield board, which is to be placed in front of a visual display screen for preventing degradation of the contrast of the displayed images by the influence of extraneous light and also for disenabling to sight the display screen from unwanted directions.
For visual displays such as cathode-ray tubes and liquid crystal displays in television sets or information systems represented by computers, various types of shade or light-shield boards have already been proposed for placement in front of the displays to restrict the angle of incidence of extraneous light to thereby prevent degradation of the contrast of the displayed pictures or characters by reflection of extraneous light. Some of hitherto proposed light-shield boards have an additional effect of limiting the angles of diffusion of light emitted from the display screen and therefore disenabling to sight the display screen from unwanted directions.
Among the above prior art, Japanese patent application primary publication No. 57-189439 (1982) shows a light-shield board consisting of a transparent substrate and an opaque film which is bonded to the transparent substrate and is formed with a number of light-transmitting apertures. The apertures have a rectangular shape and are formed in a checkered pattern, so that the opaque film exists as a grillwork. The apertured opaque film can be produced by a photolithographic method using a photosensitive resin containing a matting agent and a subsequent dyeing process. Since the opaque film has a substantial thickness, each aperture is defined by walls standing normal to the transparent substrate. Therefore, the light-shield board serves the function of limiting the angle of incidence of extraneous light on the display screen behind this board so that the contrast of the displayed images may not be degraded.
This light-shield board places a limit also on the angle of diffusion of light from the display screen. Though this is favourable for some purposes, in most cases this offers an inconvenience that the display becomes dark for a viewer whose line of sight is oblique to the light-shield board and the display screen.
There are particular cases where it is desirable to render a display screen unsightable from a specific direction. In the case of a cathode-ray tube installed in the instrument panel of an automobile for receiving television or for displaying some information such as a guide map, it will be desirable for the sake of safety to render the screen unsightable from the driver's seat while the car is running. Especially in the night the driver will be annoyed if flickering of light attributed to frequent scene transitions in the televised pictures comes into sight. On the other hand it is desirable that the screen can always be sighted from the back seat and also from the front seat next to the driver's seat. The prior art does not include a light-shield board that satisfies such desires. Therefore, it becomes necessary to employ an extra means such as placement of a shade screen between the display and the driver's seat or supplement of a mechanism to turn the picture tube itself toward the front seat next to the driver's seat.